Many injectors have been developed during the years with different degrees of functions such as automatic penetration and/or injection, setting of different doses to be injected, retractable and lockable needle shields, means for performing mixing and priming, to mention a few.
Automatic functions may have their advantages in that they reduce the actions that the user needs to perform. On the other hand an increased degree of automation and/or number of functions by necessity entails an increased number of components that need to interact with each other in reliable and repeatable ways without the risk of malfunction or break-down of the device, which otherwise could jeopardize the health of the patient. Further, the increased number of components also increases the cost of the device.
For most injectors, and for most patients, a number of actions of the injector may be performed manually, such as penetration and/or injection. However, for many drugs and administering schemes it is an advantage that the dose to be delivered may be set before injection.
One such injector is disclosed in patent application No. WO 0110484. It describes an injector having a dose setting means whereby the rear end of the injector is turned until the desired dose is displayed. The turning causes the rear part of the injector to protrude more and more out of the housing of the injector due to threads between the rear part and the housing. When the patient is to inject the medicament, he/she presses on the protruding part, whereby it is pushed back into the housing. This movement causes the protruding part to rotate back during injection.
For most patients, the force required to perform the injection is manageable where the force depends inter alia on the pitch of the threads, the resistance of the stopper inside the medicament container and the diameter of the needle channel. In that respect there is an increased demand from patients to use as small needles as possible in order to reduce the pain induced by the penetrating needle.
However, for patients/users with weak hands and fingers, with reduced manual dexterity, the force required for the injection is too high, so that they cannot operate the injector. The problem becomes more severe the longer the rear part is rotated out of the housing. Also for patients that self-inject on places on the body where they cannot see, such as in the buttock or the rear waist, having a push button on the rear of the injector is not optimal.
There is thus a demand for an injector having manual injection features that can be handled in an easy and reliable way also by patients with reduced manual dexterity as well as when the injector is held in positions where pushing on the rear end of the injector is not optimal.